Roger Cox: In the half-light, surfing is an amazing experience - in no light at all, it’s a rather scarier proposition

As Yates goes on to explain, when night comes it’s often the sudden absence of a middle-distance that causes the mind to play tricks. Even in very low light conditions you can usually see what’s going on directly in front of you and you can usually make out the horizon, but the space between those two extremes becomes something of a mystery; and rather than simply accepting this absence and working around it, the human brain sometimes decides to try and fill in the blanks, often with unhelpful results.

I was reminded of Yates’s words the other evening when, surfing at my favourite east coast watering hole well after sunset, I realised I could no longer gauge the size of the waves as they rolled towards me. The swell was only a modest one – three feet at eight second intervals – so most of the waves coming through were too small to bother with. Occasionally, though, a set of three or four shoulder-high walls would rear up out of the gloom and peel slowly along the edge of the sandbar for 20 or 30 yards before closing out with a whump on the inside.

It had been one of those rare, still evenings when even the slightest disturbance on the surface of the water sounded strangely amplified. A fish jumping ten feet away sounded like a gun going off; a seal the size of a filing cabinet cruising around just outside the breaking surf announced each fresh appearance with an ungainly flop-splash, as if, on such a lazy summer’s evening he couldn’t really be bothered to swim properly. His behaviour was so un-seal-like, in fact, that when my two surf companions Steve and Simon first spotted him there was an uneasy discussion about whether he might be a minke whale or a basking shark or... something else.

As the sun dipped behind the Bass Rock, the water changed colour from blue to highly-reflective silver, and then, as darkness crept in from the east, it lost its mercury-like quality and became a single, thick band of dark grey. Like Chris Yates on the Downs, I could see the foreground – my hands, the end of my board – and I could see the horizon. What lay between, though, was becoming increasingly difficult to judge. Steve and Simon both caught their last waves of the day and headed back to the beach, leaving me alone in the gloaming. Once or twice, I could have sworn I saw dark lines of water moving towards me. I spun around and paddled hard, then glanced over my shoulder and realised there was nothing there. On another occasion, a decent-sized wave managed to sneak up to within only a few feet of where I was sitting before I realised what was happening and hastily duck-dived out of the way. And then, in a lull between sets, I heard a loud plop as a fish jumped somewhere nearby, and suddenly I wasn’t just sitting on a two-dimensional sheet of water any more; I was suspended above a vast, three dimensional world, with a whole universe of life teeming away beneath me.

Eventually I caught a wave in, and as the three of us walked back over the dunes we joked that the next time we decided to go surfing in the dark we’d bring floodlights. We certainly wouldn’t be the first. South African surfer Mark Matthews recently set up an array of lights above a spot called Ours so he and a few mates could surf 12-footers all by themselves; and last winter Aussie surfer Mark Visser surfed the Maui deathwave commonly known as Jaws at 30 feet with only an LED surfboard to light his way. The rational part of me quite likes the idea of floodlit night-surfing – at a stroke, you’d double your chances of scoring that perfect combination of wind, tide and swell. But the irrational part of me isn’t so sure. Bobbing around on the roof of a vast underground kingdom, caught in the beam of a giant spotlight, I think I’d feel a bit uneasy – as if I was being watched from below.

• Nightwalk: A Journey to the Heart of Nature by Chris Yates is published by Collins, £14.99